Invest in an ID scanner at the gate. Ban entry to previous offenders, for life. Anyone below 16, must have an adult. Ban that adult, if the kid effs up. Get enough of them, they’ll quit coming in packs as too many of their precious homies are denied.
The Malco movie theatres did something similar when there was a riot outside their biggest theatre a few years ago here in Memphis. No one under 16 without a parent after 6 PM. No matter what movie.
They later made it a rule at all their theaters here in town.
Eighteen year old's are adults. That's not going to solve the problem.